German Patent Publication DE-OS 40 10 209 discloses a safety net arrangement that is intended to prevent objects from the cargo compartment of a passenger car or a van, hatchback or stationwagon type from being thrown into the passenger compartment, where they could injure people, in the event of a head-on collision. This known safety net arrangement comprises a safety net that is secured along one edge to a wind-up shaft that is rotatably supported in a housing to be secured to the seat back of the rear seat. The opposite edge of the safety net arrangement is provided with a loop through which a crosspiece in form of a tubular tie bar extends, and mushroom-shaped retaining members protrude from the tie bar at both ends. The mushroom-shaped retaining members are slidable longitudinally in the tie bar and are suspended by the heads of the mushrooms in suitable receptacle pockets under the roof of the car.
Adjoining the heads of the mushrooms, each retaining member is provided with a cylindrical stem, which widens radially in conical fashion on its end plugged into the tie bar. Two groups of beads or ribs pressed into the tie bar reduce the inside diameter of the tie bar towards the outside diameter of the cylindrical stem, so that the outward motion of the retaining members caused by impact of the frustoconical thickening against the farthest inward group of beads is also limited. If a rear-end collision causes an object to be thrown out of the cargo compartment against the safety net, the tie bar bends. If the energy is high, e.g. the impact force rises further, the conical thickenings press the immediately adjacent groups of inwardly extending ribs radially outwardly, thereby converting impact energy into energy required for material deformation, in order to protect the safety net from tearing.
The known arrangement has been very successful in practice in terms of the protection function it provides. Nevertheless, it involves certain limitations from the manufacturing standpoint.
In the final analysis, the wall thickness of the tube used for the tie bar depends, in each individual case, on the requisite resistance to kinking. The wall thickness of the tube varies in accordance with the width of the safety net and thus influences the stability of the ribs and consequently the work to be brought to bear in deforming the ribs or beads as well as when the force-limiting action occurs. The force-limiting action should, however, be largely independent of the safety net.
In the known structure, the ribs cannot be pressed into the tubular tie bar until after the retaining elements have been placed into the tie bar. This means that in the impressing or stamping operation, work must be done without a die, resulting in relatively wide tolerances, which in turn lead to tolerances in energy absorption. The incident tolerances upon impressing of the rib, in combination with the required radial depth of the ribs for bringing the desired force-limiting action to bear, can easily lead to excessive radial play of the retaining element stem, causing rattling noises.
The conical thickening must be produced as a separate part that is later mounted on the stem of the retaining member. This considerably increases production costs.